Surface and subsurface stratigraphic studies in northeastern Arkansas show the Calico Rock Sandstone (Middle Ordovician) to be a lobate sand body up to 200 ft thick. The environment of deposition is considered from a study of grain characteristics, ripple marks, subjacent and superjacent units and unpublished isopachous maps. The data indicate the Calico Rock Sandstone formed in a transgressing Everton sea as a barrier island and near shore sand complex. The quartz sand was derived from a northern source and was distributed by southwestward flowing longshore currents.

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